The present invention relates to an internal combustion engine having hydraulically operated valves with intake and exhaust timing parameters that are independently adjustable during engine operation.
For years, engine designers have been trying to optimize engine performance, fuel economy, and emissions control. These design goals are now largely dependent upon intake and exhaust valve timing parameters such as opening points, closing points and overlap. Valve opening and closing points are measured relative to a piston position or to a crank shaft rotation angle within a combustion cycle.
Conventional engines control valve operation and timing with a cam shaft. The cam shaft includes a cam lobe for each valve. As the cam shaft rotates, cam followers follow the circumference of each cam lobe. Each cam follower is mechanically coupled to a respective valve. Movement of the cam followers actuate the valves between opened and closed positions.
Each cylinder has an intake valve and an exhaust valve which are controlled by an intake cam lobe and an exhaust cam lobe on the cam shaft. In some designs, each cylinder includes additional intake and exhaust valves controlled by additional cams. Opening and closing points are determined by the shape of the cam lobes. Valve overlap is determined by angular positioning of the intake cam lobes with respect to the exhaust cam lobes.
In the past, the position and shape of these cam lobes were fixed. Engine designers would design the cam shaft for a selected operating torque and speed range. As a result, engine performance had to be compromised for all ranges outside the selected range.
Attempts have been made to overcome some of these design problems. In one version, the entire cam shaft is rotated relative to the engine's crankshaft to either advance or retard valve timing within the combustion cycle.
In another version, the angular positions of the intake cam lobes can be adjusted about the cam shaft relative to the exhaust cam lobes. Alternatively, the exhaust cam lobes can be adjusted relative to the intake cam lobes. The cam shaft in such a design includes an inner shaft and an outer tubular shaft. The fixed cam lobes are secured to the outer tubular shaft and the rotatable cam lobes are secured to the inner shaft. During operation, the inner shaft is rotated relative to the outer tubular shaft to vary overlap between the intake and exhaust valves.
In yet another version, the opening or closing points can be adjusted by using two-piece cam lobes. Each intake cam is divided into an opening cam lobe and a closing cam lobe. The adjustment changes the angular positioning of one of the lobes on each intake cam. Depending upon the configuration, either the opening cam lobe or the closing cam lobe may be adjusted. Alternatively, the adjustments may be made to the exhaust cam lobes. These designs have only a single phasing unit that shifts the angular position of either the inner or outer shaft. A single phasing unit does not allow adjustment of both the intake and the exhaust cam lobes relative to the crank shaft angle.
Two-phasing units allow two means of adjustment. With two phasing units, the relative angular positions of both the intake cam and the exhaust cam can be adjusted with respect to the crank shaft angle.
In yet another version, the intake and the exhaust cam lobes are two-piece cams with an opening cam lobe and a closing cam lobe. The opening cam lobe determines when the respective valve opens while the closing cam lobe determines when the valve closes. Two phasing units allow independent adjustment of the opening and closing cam lobes for either the intake cams or the exhaust cams, but not both. The two-phasing units may be controlled by digital circuitry to provide real-time adjustment of valve timing parameters based upon a number of operating variables.
Two-phasing units provide a limited choice of adjustment. Due to cost, design, and spatial constraints, it would be impractical to add any further adjustments to this type of cam shaft.
In addition, designers choose valve orientation within the engine head to optimize fuel/air flow. Valve orientation, however, is compromised because of spatial constraints and the position of the cam shaft. With mechanically operated valves, the cam shaft must be positioned close to the valves. Otherwise, the required mechanical linkage between the cam shaft and the valves is impractical. Optimum sparkplug positioning may also be compromised. These spatial constraints ultimately limit engine efficiency and power.
One method of developing more power is to move fuel/air mixture into and exhaust out of each cylinder more efficiently by having two intake and two exhaust valves per cylinder. This creates even more space problems in the engine head. More valves also require more cam lobes which makes the cam shaft design more complex. Cam lobe adjustments are therefore even more costly and impractical.
The prior art lacks a valve control system that is fully adjustable with respect to valve overlap, valve opening points, and valve closing points. The prior art further lacks a valve control system that alleviates the spatial constraints normally created by complex valve control systems.